1. Field of the Invention
The present invention relates to a control device of a high-pressure fuel system of an internal combustion engine that includes a fuel injection mechanism (in-cylinder injector) for injecting a fuel into a cylinder at a high pressure, or an internal combustion engine that includes, in addition to the above fuel injection mechanism, a fuel injection mechanism (intake manifold injector) for injecting a fuel into an intake manifold or an intake port. More particularly, the present invention relates to a high-pressure fuel supply apparatus including a high-pressure fuel pump avoiding uncomfortable feeling caused by intermittent actuation sound, as well as to a method of designing such an apparatus.
2. Description of the Background Art
An engine having a first fuel injection valve (in-cylinder injector) for injecting a fuel into a combustion chamber of a gasoline engine and a second fuel injection valve (intake manifold injector) for injecting a fuel into an intake manifold, and changing a fuel injection ratio between the in-cylinder injector and the intake manifold injector in accordance with the engine speed or the load of the internal combustion engine is known. A direct injection engine having only a fuel injection valve (in-cylinder injector) for injecting a fuel into a combustion chamber of a gasoline engine is also known. In a high-pressure fuel system including the in-cylinder injector, the fuel having its pressure increased by a high-pressure fuel pump is supplied via a delivery pipe to the in-cylinder injector, which injects the high-pressure fuel into a combustion chamber of each cylinder of the internal combustion engine.
Further, a diesel engine having a common rail fuel injection system is also known. In the common rail fuel injection system, the fuel having its pressure increased by a high-pressure fuel pump is stored in a common rail, and injected from the common rail into a combustion chamber of each cylinder of the diesel engine according to opening/closing of an electromagnetic valve.
To obtain the fuel of a high pressure in such internal combustion engines, a high-pressure fuel pump is used which has a cylinder driven by a cam provided at a driveshaft that is connected to a crankshaft of the internal combustion engine.
Japanese Patent Laying-Open No. 2001-41088 discloses a control device for a fuel pump capable of lowering continuous actuation sound caused each time an electromagnetic spill valve is closed. The control device for a fuel pump includes a fuel pump varying a volume of a pressurizing chamber based on relative movement of a cylinder and a plunger as a result of rotation of a cam, so as to suction a fuel into the pressurizing chamber and delivering the fuel to a fuel injection valve of the internal combustion engine, and an electromagnetic spill valve opening and closing a spill path for flow-out of the fuel from the pressurizing chamber. According to the control device for a fuel pump, an amount of fuel delivery from the fuel pump to the fuel injection valve is regulated by controlling a valve closing duration of the electromagnetic spill valve. The control device for a fuel pump includes a control unit for controlling the electromagnetic spill valve based on an operation state of the internal combustion engine so as to adjust the number of times of fuel delivery by the fuel pump during a prescribed period, so that the number of times of fuel injection from the fuel injection valve per one fuel delivery is changed, i.e., the number of times of fuel injection per one fuel delivery is decreased while the engine is in a low load state.
According to this control device for a fuel pump, the number of times of fuel injection per one fuel delivery is decreased while the engine is in a low load state during which continuous actuation sound is relatively high. Therefore, an amount of fuel delivered in one fuel delivery can be small. Accordingly, valve closing start timing of the electromagnetic spill valve can further be closer to the top dead center, a cam speed at the time of closing of the electromagnetic spill valve can be slower, and a sound produced when the electromagnetic spill valve is closed can further be lowered. By lowering the sound produced when the electromagnetic spill valve is closed, continuous actuation sound caused each time the electromagnetic spill valve is closed is lowered.
Japanese Patent Laying-Open No. 2001-41088 described above, however, is directed solely to lowering of continuous actuation sound in a low load state such as idling.
In such a high-pressure fuel system, a check valve provided with a leakage function is provided in the electromagnetic spill valve closer to a high-pressure pipe side. The check valve provided with the leakage function is a check valve of a normal type but provided with pores that are always open. Accordingly, when a fuel pressure within the high-pressure fuel pump becomes lower than a fuel pressure within the high-pressure delivery pipe (for example, when the engine and hence the cam stops while the electromagnetic spill valve remains open), the high-pressure fuel within the high-pressure delivery pipe returns through the pores back to the high-pressure fuel pump side, thereby lowering the fuel pressure within the high-pressure delivery pipe. As such, at the time of stop of the engine, for example, the fuel within the high-pressure delivery pipe is not at a high pressure, so that leakage of the fuel from the in-cylinder injectors can be prevented.
Depending on an amount of leakage in the check valve provided with the leakage function, the high-pressure pump may intermittently operate. Namely, when the fuel pressure becomes too high, the fuel pressure is controlled in a feedback manner by a fuel pressure sensor provided at the high-pressure delivery pipe, drive duty of the electromagnetic spill valve is set to 0%, and the electromagnetic spill valve remains open. Though a pump plunger slides up and down as long as the cam continues to rotate (along with revolution of the engine), the electromagnetic spill valve does not close, in which case the fuel is not pressurized. Thereafter, when the fuel pressure becomes too low, the drive duty of the electromagnetic spill valve is no longer set to 0%, the electromagnetic spill valve closes, and the fuel is pressurized.
If an amount of leakage in the check valve provided with the leakage function structured as above is inappropriate, the high-pressure pump is intermittently actuated (a period during which actuation sound caused by a valve closing operation of the electromagnetic spill valve is not produced and a period during which the actuation sound is produced are repeated at certain intervals), irregular actuation sound is produced, and a driver or the like may feel uncomfortable. That is, as a result of intermittent actuation of the high-pressure pump, sound from the engine is changed, which results in uncomfortable feeling. In particular, such uncomfortable feeling is strongly felt outside a vehicle during idling.